Electrical-resistance wire



A H. JOHNSON.

ELECTRICAL RESISTANCE WIRE.

APPLICATION FILED DEC. 19. 1919.

1 ,3 14 A OG, Patented June 22. 1920 loops and intermediate,

bent or crimped to UNITED STATES NATIONAL ELECTRICAL SUPPLY COMPANY, OFCOLUMBIA, AIJORPORATION OF VIRGINIA.

OF COLUMBIA, ASSIGNOR TO WASHINGTON, DISTRICT OF ELECTRICAL-RESISTANCEWIRE.

Specification of Lettersratent. Patented J 11113 22, 1920.

Application filed December 19, 1919. Serial No. 345,972.

To all '10 from it may concern:

Be it known that I, Annnnr I'I. JorrNsoN, a citizen of the UnitedStates, residing at \Vashington, in the District of Columbia, haveinvented certain new and useful Improvements in lllectrical-licsistance\Vire, of which the following is a specification.

This invention relates to electrical resistance elements, and itcomprises a resistance element made of substantially circular wire, saidwire being bent or crimped to form connecting sections between saidloops, the connecting sections being flattened on opposite sides, andsaid flattened surfaces being corrugated or roughened; all as more fullyhereinafter set forth and as claimed. I

In the manufacture of electric heating appliances wire having a highdegree of resistance is employed. This wire is generally form loops andconnecting sections between the loops, producing substantially U-shapedportions, with inverted Ushaped portions therebetween, the legs of theU-shaped portions being connected to the adjacent inverted U-shapedportions. The units are generally arranged in a substantially circularform by bending the unit near the center to produce substantiallyparallel sections, and then forming the unit into a spiral, with thebent portion at the center of the spiral, and the two ends at theperiphery thereof. When a plurality of these coils are employed, theyare arranged on top of each other with a strip or sheet of mica, orother insulating material, separating them.

W hen: wire of substantially circular cross section is crimped in thismanner, and is then bent in any particular manner to give it a certainexternal shape, there is a strong possibility of the individual loopscoming in contact with each other on the inside of the bend. Inelectrical resistance elements and especially where the-loops arearranged in a flat spiral, this tendency is noted and it is necessary toavoid it. If two sections of the wire touch each other, one of the loopsis short circuited and the current does not pass through it. The resultis that the amount of heat that the loop is estimated to furnish is notobtained.

I have found that where the-sides of a loop are first flattened toproduce elongated sections, that this ditliculty of short circuiting isavoided and that the rounded ends of the loops 'are kept spaced fromeach other.

Another important advantage of my invention is obtained where a numberof heating elements are employed, arranged one above the other andseparated from each other by thin strips of mica or other insulatingmaterial. \Vith a unit of wire in which the cross section of theindividual loops is substantially circular, there is a tendency of themica plates to move relative to the units and thus permit the units tocome in contact with each other. If the in sulation on the wiringbecomes worn at any point, short circuiting occurs from one unit to theother. 1

Where the sides of the loops are flattened to produce elongatedsections, this tendency of the insulating strip to work out of positionis greatly diminished. Furthermore,

I have found that roughening the sides forming the elongated sections,practically eliminates the tendency of the insulating strips to move.hen a heating element consisting of several units is assembled, a

slight amount of pressure may be applied as each strip of mica or otherinsulating material is being put in place, causing the roughenedportions of the resistance element to embed a slight distance in themica and thus eliminate any tendency to relative movement.

In the accompanying drawings, I have shown one embodiment of thisinvention.

In this showing,

Figure 1 is a plan view of an electrical resistance element wherein thesides of the individual loops have been flattened.

Fig. 2 is a sectional view on the line 2-2 of Fig. 1.

Fig. 3 is a sectional view on the line 33 of Fig. 1, and

Fig. 4 is a plan View of a resistance element formed of flattened androughened resistance wire.

Referring to the drawings, the reference numeral 1 designates a strip ofwire that has been bent back and forth to produce 100 s 2. These loopsare connected by interme l tened on the two outer sides, as shown at 4and 5. The sections 3 maybe flattened by passing the wire between tworolls and ap plying pressure thereto, or by any other desired method.After the sides have been flattened, they may be passed between twoother rollers having roughened surfaces for the purpose of crimping orroughening the surface of these sections, or the surfaces of the firstmentioned rolls may be roughened, in which case the flattening andrough'ening of the wire are brought about in a simple operation. Inpractice,l prefer to follow the latter practice. The roughened portionis designated by the reference numeral 6 and is more clearly shown inFig. 3 of the drawings.

In Fig. 4 of the drawings, I have shown for the purpose of illustrationthe ordinary form ofa resistance unit wherein the strip of wire is firstbent at a point 7 near its mid- -dle to produce two substantiallyparallel sections. These parallel sections are then formed into a spiral8 with the ends 9 and 10 arranged at the outside of the spiral. Byreference to this figure, it will be noted that there is a tendency in aheating unit of this character for the loops 2 to contact with eachother at the inside of a bend, such .as at the points 11 and 12. I havefound that the flattening of the connecting portions 3 prevents contactof adjacent loops when the device is bent into the form of a spiral.

When it is desired to produce a heating unit of greater capacity thancan be obtained from a single resistance element, it is customary toarrange several of the heating elements shown in Fig. 4 upon each otherand to separate them by strips of mica or other insulating material.WVhen the wire employed in constructing the elements is of substantiallycircular cross section, there is a tendency of the mica strips to becomedisplaced and to permit contact of one element with the element nextabove it. I have found that flattening the connecting sections of thewire employed in constructing such resistance elements, as at 4 and 5 inthe drawings, greatly reduces this tendency of the mica plates to becomedisplaced. When these flattening portions are roughened, the tendency ofthe insulation to become displaced can be entirely overcome. When theheating unit is assembled, the mica; plates are placed on the top of aunit and a sli ht amount of pressure applied thereto. his pressurecauses the roughened surface 6 to engage the surface of the mica andhold it firmly. Under such condition, the mica is held in its properposition and relative movement is entirely eliminated.

In the description and drawings, I have shown one advantageousembodiment of my invention, but it is apparent that the invention is notnecessarily limited to the exact form shown and described, and thatchanges may be made without departing from the spirit of the inventionor the claims.

\V hat I claim is:

1. An electrical resistance element comprising loops of wire ofsubstantially circular cross section and connecting sections, theconnecting sections being flattened to produce oppositely disposedelongated sections.

2. An electrical resistance element comprising loops of wire ofsubstantially circular cross section and connecting sections, tireconnecting sections being flattened to pi'roduce oppositely disposedelongated sect ons, said elongated sections being roughened.

3. An electrical resistance element comprising loops of wire,substantially circular in cross section, and connecting sections, saidloops being arranged to produce a re- .sistance element of any desiredshape, said connecting sections being flattened on the top and bottom.

4. An electrical resistance element comprising loops of wire,substantially circular in cross section, and connecting sections, saidloops being arranged to produce a resistance element of any desiredshape, said connecting sections being flattened on the top and bottom,and said sections being roughened.

5. The method of constructing electrical resistance elements which comrises arranging a resistance wire in the fbrmof loops and connectingsections, of substantially circular cross section, and flattening twosides of said connecting sections to produce oppositely disposedelongated sections.

6. The method of constructing electrical resistance elements whichcomprises arranging a resistance wire in the form of loops and connectig sections, of substantially circular cross I ction, flattening twosides of said connect ng sections to produce oppositely disposedelongated sections, and roughening said elongated sections.

In testimo'n whereof I afiix my signature in presence (5 two witnesses.

ALBERT H. JOHNSON.

Witnesses:

I CHAS. O. REED,

CORNELIA KLUETER.

